I looked that up and seems many people have the same problem with no solution. People have suggested a bad ignition switch, removable faceplate (if equipped) has came unlatched and needs snapping back in or fuses. If it has a clock then it has power running to it all the time for the memory only.
I suggest ditching it and installing a new one. I just bought a new Kenwood for my truck from Crutchfield
that came with all adapters, both wiring and mounting along with step by step instructions that made it a piece of cake.